PIN diode

PIN diode switches exploit the same charge-storage phenomenon that's responsible for the reverse recovery behaviour of the diode.

It's a transport phenomenon, governed by an integral equation that isn't reducible to a system of ODEs, so you're right, SPICE can't simulate it for real. (The reason is that the diode has internal state that isn't instantaneously visible at the pins.) It can be phonied up over some range of parameters, of course.

Some years ago the late lamented JT, some others, and I had a big argument here on this very point.

Cheers

Phil Hobbs

That would be so with a Schottky or very fast junction diode. The point of using PIN diodes is that even with a DC current much less than the peak RF current, an RF half-cycle transfers only a small portion of the stored charge in the junction, so the diode hardly notices.

Cheers

Phil Hobbs

Am 21.10.21 um 01:15 schrieb John Larkin:

you won't get a spice model because spice does not understand carrier lifetime which is crucial for PIN diode operation. You can easily get a Keysight ADS or a MWO model.

But getting ADS or MWO will set you back > $100K unless you know the net and have enough criminal energy. ;-)

Gerhard

What's extra weird to me is that a regular diode would have a dynamic resistance around 5 ohms at 5 mA DC. But that Macom PIN diode is about

The mental model of a regular diode with an unusually wide I region doesn't seem to work.

Am 21.10.21 um 03:12 schrieb Gerhard Hoffmann:

To make the Ingrid: I would not call it fiddling, applying the S-parameters and assume 20 mA DC through the diode, or -10V across.

Gerhard

(Ingrid was a women in the German sub-internet who was famous for endless auto-follow-ups where you could follow every step of her thinking...)

And I already proposed QUCS studio as a simulator that also handles S-parameters. <

Yes, thanks, JL also pointed that out.

That must also be relevant to how the Skyworks limiter diodes work too. Once they turn on, they stay on in both directions for a number of cycles at least.

CH

The point

And it's an important diagnostic tool, to be able to sweep (slowly) the bias while probing the RF capacitance; it tells you the doping profile of the junction. 'Hyperabrupt' doping gives the biggest capacitance variation, good for varactors.

The NanoVNA does TDR.

Badly, by transforming the frequency/impedance response. Nothing like a real TDR.

I wonder. I haven't looked at this device in particular, but when I use the FT feature on my HP8753D VNA, the TDR trace is _much_ cleaner than the trace from my Tek S6 sampler and S52 pulser combination. You can't beat a VNA for S/N.

Granted, you don't expect HP8753-class quality from a NanoVNA.

Jeroen Belleman

Ebers-Moll works in the low-frequency limit, where carrier lifetime isn't an issue. Carrier dynamics can do funny things, as you have good reason to know. ;) (*)

Cheers

Phil Hobbs

(*) Grekhov and all that

The doping density is related to the second derivative of C(V), but I've never heard of doing that measurement at forward bias, let alone at RF.

Cheers

Phil Hobbs

Most semiconductor effects were discovered largely by accident, theory later. Diodes, bipolar transistors, SRDs, DSRDs, apparently the tunnel diode.

I guess most physics was like that too.

Later generation Tek TDR is much better. And you can smooth and signal average to improve s/n if you really need to.

A dual-channel SD24 TDR head is a nice combination pulse generator and scope, DC to 20 GHz.

Is a VNA tdr realtime? I like to run my finger along a trace and follow the TDR, to locate vias and corners and such.

I can also touch things with a pencil and instantly see exactly where features are.

More modern devices such as 'quantum dots' as well as the pHEMT and other "2D electron gas" structures came out of theoretical ideas first, once the basic approximations to the quantum mechanics of solid state devices were worked out.

Cheers

Phil Hobbs

Yeah, you'd have to clean up column contents to do R or Vf sorting. Not all parts have either. R~Rf forward conduction impedance Vf usually a maximum forwad voltage T - typical. As a quality of the part, whatever was offered in the data sheet is entered into the table. This is a quick tool to get part numbers in the ballpark.

RL

No, the HP8753 has a pretty wimpy processor, so updates are slow. A real TDR clearly wins out there.

It's not so long ago that I realized I can drive the 7T11 sampler time base plug-in with a DAC to control the sweep and read-out the

Jeroen Belleman

I don't think a standard PIN data sheet (or diode, for that matter) is going to help you much, if you intend to use <5V as bias.

You must be anticipating mV signal levels . . . then why a PIN?

RL